Formation of Multigradient Porous Surfaces for Selective Bacterial Entrapment

Herein we describe the preparation of multigradient porous platforms by using the breath figures approach. In a single and straightforward step, we prepared porous surfaces in which three different parameters vary gradually from the edge of the sample to the center in a radial manner. Thus, we evidenced the gradual variation of the pore size and the shape of the pores that can be varied, depending on the sample concentration, but also depending on their radial position within the same sample. In addition, we succeeded in the control over the chemical composition inside and outside the pores as well as the variation of the concentration of block copolymer inside the pores as a function of their radial position. Moreover, the chemical composition and the variable cavity size of porous surfaces have been evaluated to analyze the influence of these variables on the selective bacterial immobilization. To the best of our knowledge this is the first example in which, by using a simple one-step strategy, a multigradient surface can be obtained. These initial results can be the base to construct platforms for selective immobilization and isolation of bacteria.Peer Reviewe

Anisotropic Thermal Diffusivity and Conductivity in La-Doped Strontium Niobate Sr2Nb2O7

The thermal diffusivity of the La-doped layered perovskite Sr2Nb2O7 parallel and perpendicular to the perovskite layers is reported from room temperature up to 1000°C. The anisotropy persists through an incommensurate-normal ferroelectric phase transformation at 215°C and up to 1000°C, the maximum temperature of our measurements. The thermal conductivity perpendicular to the perovskite layers, derived from the diffusivity in the same direction, calculated using the density and measured heat capacity, has a constant value of 1.05±0.05 W/mK up to 1000°C. Possible explanations for the low thermal conductivity and anisotropy are described.Engineering and Applied Science

Physical, Electrical, and Piezoelectric Properties of Hot-Forged Sr₂(NbTa)₂O₇ Ceramics

ABSTRACTSolid solution compositions of Sr2(NbxTa1−x)2O7 ceramics with Tr ranging from 450°C to 1342°C were fabricated utilizing a hot-forging technique to achieve preffered grain orientation and thus enhance poling. Translucent samples with greater than 99% theoretical density were obtained using this process. Depending on composition, the degree of orientation as determined by x-ray diffraction was found to be 75% to 95%. The thermal expansion, resistivity, and dielectric constant were shown to be very anisotropic. The direction perpendicular to the forging axis proved to be the ferroelectric “easy” direction, exhibiting hysteresis behavior. Piezoactivity in PLS polycrystals was measured for the first time. Hot-forged samples were electrically poled and the electromechanical properties determined using the five different modes of vibration. For Sr2(Nb0.5Ta0.5)2O7: N24=1504 Hz-m, s44=18.2×10-12m2/N, k24=3.0%, d24=2.6 pC/N, g24=6.3×10-3 Vm/N, and Qm=1100. This material was also shown to resist depoling when exposed to temperatures as high as 650°C.</jats:p